The definitive book on the subject: Neil Rosenberg, "Bluegrass: A History." Available wherever good books are sold. (My copy is so worn out I really should get a new one.)
There is also a shorter book by the same guy who wrote the Monroe bio, Richard Smith. It's just called "Bluegrass" iirc. A nice overview.
Then there are various books about the Carter family, Ralph Stanley, and others. There's a book called "The Bill Monroe Reader" edited by Tom Ewing, quite nice. There's a nice little book about Jimmy Martin by Tom Piazza, quite funny.
That should get you started. The Monroe bio is, by the way, one of the better books I've read, and an excellent biography.
J. Mark Lane
Stanley #10 F5
Pomeroy #72 F4
Brian Dean #30 Bowlback